Method for controlling linear compressor and refrigerator

ABSTRACT

A method for controlling a linear compressor and a method for controlling a refrigerator are provided. The method for controlling a linear compressor may include measuring an ambient temperature, and when the measured ambient temperature is equal to or lower than a predetermined safety temperature, applying a safety current to a motor assembly for driving a piston. On the other hand, when the measured ambient temperature is higher than the predetermined safety temperature, a current lower than the safety current may be applied to the motor assembly.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims the benefit of priority to Korean Patent Application No. 10-2018-0109707, filed in Korea on Sep. 13, 2018, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND 1. Field

A method for controlling a linear compressor and a method for controlling a refrigerator are disclosed herein.

2. Background

In general, a refrigerator is a home appliance which is capable of storing food at a low temperature in a storage chamber inside the refrigerator, which is shielded by a door. The refrigerator is provided with a cooling system, and an inside of the storage chamber is maintained at a temperature lower than an external temperature.

The cooling system is a system that generates cold air by circulating a refrigerant, and repeatedly performs compression, condensation, expansion, and evaporation processes of the refrigerant. The cooling system includes a compressor, a condenser, an expansion device, and an evaporator.

In general, a compressor is a mechanical device that increases pressure by receiving power from a power generating device, such as an electric motor and a turbine, to compress air, refrigerant, or other various working fluids, and is widely used throughout the industry in addition to home appliances such as the refrigerator. The compressor is divided into a reciprocating compressor, a rotary compressor, and a scroll compressor according to the compression method of the working fluid.

The reciprocating compressor includes a cylinder and a piston provided in the cylinder to linearly reciprocate. A compression space is formed between the piston head and the cylinder, and the working fluid in the compression space is compressed to high temperature and high pressure while the compression space is increased and decreased by the linear reciprocating motion of the piston.

Recently, among the reciprocating compressors, development of a linear compressor to directly connect the piston to the reciprocating linear motor has been actively made. The linear compressor is configured to suction the refrigerant into the compression space, compress, and then discharge the refrigerant while the piston is linearly reciprocated in the cylinder by the linear motor inside the sealed shell. In addition, the linear compressor may be provided as an oilless compressor using a refrigerant as a bearing without working oil.

In relation to the oilless linear compressor as described above, the applicant has filed a prior document, Korean Publication Number: No. 10-2018-0093526, published Aug. 22, 2018, which is hereby incorporated by reference. The prior document discloses a structure in which at least some of the refrigerant compressed by the piston (hereinafter, the “bearing refrigerant”) is provided to the piston through the frame and the cylinder.

In a case where the bearing refrigerant is not sufficiently supplied, there is a problem that it does not function as a bearing. Accordingly, various problems may occur such that the piston does not operate normally and is damaged by friction.

In particular, when an ambient temperature of the linear compressor is very low, the bearing refrigerant does not function as a bearing. Specifically, as the ambient temperature is lowered, the amount of refrigerant flowing through the linear compressor is reduced, thereby reducing the amount of the bearing refrigerant. Therefore, there is a problem that the bearing refrigerant does not provide the floating force to the piston.

In addition, as the ambient temperature is lowered, the temperature of the bearing refrigerant may be lowered and condensed. As the bearing refrigerant is condensed, the bearing flow path formed in the frame or the cylinder may be closed. Therefore, there is a problem that the bearing refrigerant is not supplied to the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein:

FIG. 1 is a view illustrating a refrigerator according to an embodiment;

FIG. 2 is a view illustrating an outer appearance of the linear compressor according to an embodiment;

FIG. 3 is an exploded view illustrating a shell and a shell cover of the linear compressor according to an embodiment;

FIG. 4 is an exploded view illustrating a configuration of the linear compressor according to an embodiment;

FIG. 5 is a view illustrating a section taken along the line V-V′ of FIG. 2;

FIG. 6 is a view illustrating a control configuration of the linear compressor according to an embodiment;

FIGS. 7 and 8 are views illustrating a control flow of the linear compressor according to an embodiment; and

FIG. 9 is a view illustrating a control flow of a refrigerator having a linear compressor according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are illustrated in different drawings. In addition, in describing the embodiments, when it is determined that a detailed description of a related well-known configuration or function interferes with the understanding of the embodiments, the detailed description thereof will be omitted.

In addition, in describing the components of the embodiments, terms such as first, second, A, B, (a), and (b) may be used. These terms are only for distinguishing the components from other components, and the nature, sequence, or order of the components are not limited by the terms. If a component is described as being “connected”, “coupled” or “accessed” to another component, that component may be directly connected or accessed to that other component, but It is to be understood that another component may be “connected”, “coupled” or “accessed” between each component.

FIG. 1 is a view illustrating a refrigerator according to an embodiment. As illustrated in FIG. 1, the refrigerator 1 according to an embodiment may include a cabinet 2 forming an outer appearance and at least one refrigerator door 3 coupled to the cabinet 2.

At least one storage chamber 4 may be provided inside of the cabinet 2. The refrigerator door 3 may be rotatably or slidably connected to a front surface of the cabinet 2 to open and close the storage chamber 4. The storage chamber 4 may include at least one of a refrigerating chamber or a freezing chamber, and each chamber may be partitioned by a partition wall.

In addition, the inside of the cabinet 2 may be provided with a machine room 5 in which a compressor 10 may be disposed. As illustrated in FIG. 1, the machine room 5 may be disposed at a lower rear side of the cabinet 2. In FIG. 1, the arrangement of the compressor 10 is merely exemplary, and the compressor 10 may be disposed at various places.

In addition, the compressor 10 may be provided as a linear compressor which is a kind of reciprocating compressor. The linear compressor may be installed in various devices, such as an air conditioner, as well as the refrigerator 1 to form a refrigeration cycle.

Hereinafter, a linear compressor according to an embodiment will be described.

FIG. 2 is a view illustrating an outer appearance of a linear compressor according to an embodiment. FIG. 3 is an exploded view illustrating a shell and a shell cover of the linear compressor according to an embodiment.

Referring to FIGS. 2 and 3, the linear compressor (hereinafter, “compressor 10”) according to an embodiment may include a shell 101, and shell covers 102 and 103 coupled to the shell 101. In a broad sense, the shell covers 102 and 103 may be understood as one configuration of the shell 101.

Legs 50 may be coupled to a lower side of the shell 101. The leg 50 may be coupled to a base of a product on which the compressor 10 is installed. In other words, the leg 50 may be coupled to the machine room 5 of the refrigerator 1 described above.

The shell 101 may have a substantially cylindrical shape and an arrangement lying in a transverse direction, or an arrangement lying in an axial direction. Referring to FIG. 2, the shell 101 extends lengthwise in a horizontal direction and may have a somewhat lower height in a radial direction.

In other words, as the compressor 10 may have a low height when the compressor 10 is installed in the machine room 5 of the refrigerator 1, there is an advantage that a height of the machine room 5 may be reduced. Thereby, a volume of the storage chamber 4 in the cabinet 2 of a same volume may be increased.

On an outer surface of the shell 101, a terminal 108 may be installed. The terminal 108 is understood as a component for delivering external power to motor assembly 140 (see FIG. 4) of the linear compressor. In particular, the terminal 108 may be connected to a lead wire of coil 141 c (see FIG. 4).

On an outside of the terminal 108, bracket 109 may be installed. A plurality of brackets surrounding the terminal 108 may be included. The bracket 109 may perform a function of protecting the terminal 108 from external shock, for example.

Both side portions of the shell 101 may be configured to be open. The shell covers 102 and 103 may be coupled to both side portions of the open shell 101. The shell covers 102 and 103 may include first shell cover 102 coupled to an open or first side portion of the shell 101 and second shell cover 103 coupled to the other open or second side portion of the shell 101. By the shell covers 102 and 103, an inner space of the shell 101 may be sealed.

With reference with FIG. 2, the first shell cover 102 may be located at a right or first side portion of the compressor 10, and the second shell cover 103 may be located at a left or second side portion of the compressor 10. In other words, the first and second shell covers 102 and 103 may be disposed to face each other.

The compressor 10 may further includes a plurality of pipes 104, 105, and 106 provided in the shell 101 or the shell covers 102 and 103 to suction, discharge, or inject refrigerant. The plurality of pipes 104, 105, and 106 may include a suction pipe 104 which allows the refrigerant to be suctioned into an inside of the compressor 10, a discharge pipe 105 which allows the compressed refrigerant to be discharged from the compressor 10, and a process pipe 106 for replenishing the compressor 10 with the refrigerant.

For example, the suction pipe 104 may be coupled to the first shell cover 102. The refrigerant may be suctioned into the compressor 10 in the axial direction through the suction pipe 104.

The discharge pipe 105 may be coupled to an outer circumferential surface of the shell 101. The refrigerant suctioned through the suction pipe 104 may be compressed while flowing in the axial direction. In addition, the compressed refrigerant may be discharged through the discharge pipe 105. The discharge pipe 105 may be disposed at a position closer to the second shell cover 103 than the first shell cover 102.

The process pipe 106 may be coupled to the outer circumferential surface of the shell 101. A worker may inject refrigerant into the compressor 10 through the process pipe 106.

The process pipe 106 may be coupled to the shell 101 at a different height from the discharge pipe 105 to avoid interference with the discharge pipe 105. The height is understood as a distance in a vertical direction (or radial direction) from the leg 50. As the discharge pipe 105 and the process pipe 106 are coupled to the outer circumferential surface of the shell 101 at different heights, work convenience may be achieved.

At least a portion of the second shell cover 103 may be positioned to be adjacent to an inner circumferential surface of the shell 101, corresponding to a point at which the process pipe 106 is coupled. In other words, at least a portion of the second shell cover 103 may act as a resistance of the refrigerant injected through the process pipe 106.

Therefore, at a viewpoint of a flow path of the refrigerant, a flow path size of the refrigerant flowing through the process pipe 106 is decreased by the second shell cover 103 while entering the inner space of the shell 101 and again increases while passing through the inner space of the shell 101. In this process, the pressure of the refrigerant may be reduced to vaporize the refrigerant.

On the inner surface of the first shell cover 102, a cover support portion or support 102 a may be provided. A second support device 185 described hereinafter may be coupled to the cover support portion 102 a. The cover support portion 102 a and the second support device 185 may be understood as a device for supporting a main body of the compressor. Here, the main body of the compressor means a component provided in the shell 101, for example, which may include a drive unit for back and forth reciprocating motion and a support portion for supporting the drive unit.

The drive unit may include components such as a piston 130, a magnet frame 138, a permanent magnet 146, a supporter 137, and a suction muffler 150 described hereinafter. The support portion may include components such as resonant springs 176 a and 176 b, a rear cover 170, a stator cover 149, a first support device or support 165, and a second support device or support 185, for example, which will be described hereinafter.

On the inner surface of the first shell cover 102, a stopper 102 b may be provided. The stopper 102 b is understood as a component which prevents the main body of the compressor, in particular, the motor assembly 140, from colliding with the shell 101 and being damaged by vibration or shock generated during transportation of the compressor 10. The stopper 102 b may be positioned adjacent to the rear cover 170 described hereinafter, and when shaking occurs in the compressor 10, the rear cover 170 interferes with the stopper 102 b, thereby preventing the shaking from being transmitted to the motor assembly 140.

On the inner circumferential surface of the shell 101, a spring fastening portion or fastener 101 a may be provided. For example, the spring fastening portion 101 a may be disposed at a position adjacent to the second shell cover 103. The spring fastening portion 101 a may be coupled to first support spring 166 of the first support device 165 which will be described hereinafter. By coupling the spring fastening portion 101 a and the first support device 165, the main body of the compressor 10 may be stably supported inside the shell 101.

FIG. 4 is an exploded view illustrating a configuration of the linear compressor according to an embodiment. FIG. 5 is a view illustrating a section taken along the line V-V′ of FIG. 2.

Referring to FIGS. 4 and 5, the compressor 10 according to an embodiment may include a cylinder 120, piston 130 which reciprocates linearly movement in an interior of the cylinder 120, and motor assembly 140 for imparting a drive force to the piston 130.

In addition, the compressor 10 may further include suction muffler 150 which is connected to the piston 130 and which reduces noise generated from refrigerant suctioned through the suction pipe 104. The refrigerant suctioned through the suction pipe 104 may flow into the piston 130 through the suction muffler 150. For example, in a process of passing the refrigerant through the suction muffler 150, the flow noise of the refrigerant may be reduced.

The suction muffler 150 may include a plurality of muffler 151, 152, and 153. The plurality of mufflers 151, 152, and 153 may include first muffler 151, second muffler 152, and third muffler 153 coupled to each other.

The first muffler 151 may be located inside the piston 130, and the second muffler 152 may be coupled to a rear side of the first muffler 151. The third muffler 153 may accommodate the second muffler 152 therein and may extend to a rear of the first muffler 151. In view of a flow direction of the refrigerant, the refrigerant suctioned through the suction pipe 104 may pass through the third muffler 153, the second muffler 152, and the first muffler 151 in order. In this process, flow noise of the refrigerant may be reduced.

A muffler filter (not illustrated) may be positioned at an interface at which the first muffler 151 and the second muffler 152 are coupled to each other. For example, the muffler filter may have a circular shape, and an outer circumferential portion of the muffler filter may be supported between the first and second mufflers 151 and 152.

Hereinafter, for convenience of description, the direction is defined. The term “axial direction” may be understood as a direction in which the piston 130 reciprocates, that is, a transverse direction in FIG. 5. In the “axial direction”, the direction from the suction pipe 104 toward the compression space P, that is, the direction in which the refrigerant flows, is referred to as a “frontward direction”, and the opposite direction thereto is defined as a “rearward direction”. For example, when the piston 130 moves forward, the compression space P may be compressed. On the other hand, the “radial direction”, which is a direction perpendicular to the direction in which the piston 130 reciprocates, can be understood as a longitudinal direction of FIG. 5.

The piston 130 may include a substantially cylindrical piston main body 131 and a piston flange 132 extending from the piston main body 131 in the radial direction. The piston main body 131 may reciprocate in the cylinder 120, and the piston flange 132 may reciprocate outside of the cylinder 120. In addition, the piston 130 may include a suction hole 133 through which the refrigerant flows and a suction valve 135 which opens and closes the suction hole 133. The suction hole 133 may be formed in or at a front portion of the piston main body 131.

The piston 130 may further include a valve fastening member or fastener 134 for fastening the suction valve 135 to the piston 130. The valve fastening member 134 may be coupled to the front portion of the piston main body 131 by passing through the suction valve 135.

The cylinder 120 may receive the piston 130. The cylinder 120 may be configured to receive at least a portion of the first muffler 151 and the piston main body 131. Inside the cylinder 120, compression space P through which the refrigerant is compressed by the piston 130 is formed.

The compressor 10 may include a discharge cover 160 and discharge valve assembly 161 and 163. The discharge cover 160 may be installed in front of the compression space P to form a discharge space 160 a through which the refrigerant discharged from the compression space P flows. The discharge space 160 a may include a plurality of space portions or spaces partitioned by an inner wall of the discharge cover 160. The plurality of space portions may be disposed in the frontward and rearward direction and may communicate with each other.

The discharge valve assemblies 161 and 163 may be coupled to the discharge cover 160 and selectively discharge the refrigerant compressed in the compression space P. The discharge valve assembly 161 and 163 may include discharge valve 161 which is opened when the pressure of the compression space P becomes equal to or higher than a discharge pressure to allow refrigerant to flow into the discharge space 160 a and spring assembly 163 provided between the discharge valve 161 and the discharge cover 160 to provide an elastic force in the axial direction.

The spring assembly 163 may include a valve spring 163 a and a spring support portion or support 163 b that supports the valve spring 163 a on the discharge cover 160. For example, the valve spring 163 a may include a leaf spring. The spring support portion 163 b may be injection-molded integrally with the valve spring 163 a by an injection process, for example.

The discharge valve 161 may be coupled to the valve spring 163 a, and a rear portion or a rear surface of the discharge valve 161 may be positioned to be capable of being supported on the front surface of the cylinder 120. When the discharge valve 161 is supported on the front surface of the cylinder 120, the compression space P may be kept closed, and when the discharge valve 161 is spaced apart from the front surface of the cylinder 120, the compression space P may be opened, and the compressed refrigerant in the compression space P may be discharged.

The compression space P may be understood as a space formed between the suction valve 135 and the discharge valve 161. In addition, the suction valve 135 may be formed at one or a first side of the compression space P, and the discharge valve 161 may be provided on the other or a second side of the compression space P, that is, on the opposite side of the suction valve 135.

In the process of reciprocating linear movement of the piston 130 in the interior of the cylinder 120, when the pressure of the compression space P is equal to or lower than a suction pressure, the suction valve 135 is opened and the refrigerant is suctioned into the compression space P. On the other hand, when the pressure of the compression space P is equal to or higher than the suction pressure, the refrigerant in the compression space P is compressed in a state in which the suction valve 135 is closed.

On the other hand, when the pressure of the compression space P is equal to or higher than the discharge pressure, the valve spring 163 a is deformed forward while opening the discharge valve 161, the refrigerant is discharged from the compression space P and is discharged to the discharge space of the discharge cover 160. When the discharge of the refrigerant is completed, the valve spring 163 a provides a restoring force to the discharge valve 161 so that the discharge valve 161 is closed.

The cover pipe 162 a may be coupled to the discharge cover 160 to discharge the refrigerant flowing in the discharge space 160 a of the discharge cover 160. For example, the cover pipe 162 a may be made of a metal material.

A loop pipe 162 b may be coupled to the cover pipe 162 a to transfer the refrigerant flowing through the cover pipe 162 a to the discharge pipe 105. One or a first side of the loop pipe 162 b may be coupled to the cover pipe 162 a and the other or a second side thereof may be coupled to the discharge pipe 105.

The loop pipe 162 b may be made of a flexible material and may be formed to be relatively long. In addition, the loop pipe 162 b may extend roundly from the cover pipe 162 a along the inner circumferential surface of the shell 101 to be coupled to the discharge pipe 105. For example, the loop pipe 162 b may have a wound shape.

The compressor 10 may further include frame 110. The frame 110 may be understood as a component for fixing the cylinder 120. For example, the cylinder 120 may be press-fitted inside the frame 110. The cylinder 120 and the frame 110 may be made of aluminum or an aluminum alloy material, for example.

The frame 110 may be disposed to surround the cylinder 120. In other words, the cylinder 120 may be received inside the frame 110. In addition, the discharge cover 160 may be coupled to a front surface of the frame 110 by a fastening member.

The cylinder 120 may include a cylinder main body 121 extending in the axial direction and a cylinder flange 122 provided outside of a front portion of the cylinder main body 121. The cylinder main body 121 has a cylindrical shape having a central axis in the axial direction and is inserted into the frame 110. Therefore, an outer circumferential surface of the cylinder main body 121 may be positioned to face an inner circumferential surface of the frame 110.

The motor assembly 140 may include an outer stator 141 fixed to the frame 110 and disposed to surround the cylinder 120, an inner stator 148 spaced apart from the inside of the outer stator 141, and permanent magnet 146 positioned in the space between the outer stator 141 and the inner stator 148. The permanent magnet 146 may be linearly reciprocated by the mutual electromagnetic force between the outer stator 141 and the inner stator 148. In addition, the permanent magnet 146 may be composed of a single magnet having one pole or a plurality of magnets having three poles.

The permanent magnet 146 may be installed in the magnet frame 138. The magnet frame 138 may have a substantially cylindrical shape and may be inserted into a space between the outer stator 141 and the inner stator 148.

With reference to the sectional view of FIG. 5, the magnet frame 138 may be coupled to the piston flange 132, extend in an outer radial direction, and be bent forward. The permanent magnet 146 may be installed in or at a front portion of the magnet frame 138. Accordingly, when the permanent magnet 146 reciprocates, the piston 130 may reciprocate in the axial direction together with the permanent magnet 146.

The outer stator 141 may include coil winding bodies 141 b, 141 c, and 141 d and a stator core 141 a. The coil winding bodies 141 b, 141 c, and 141 d may include bobbin 141 b and coil 141 c wound in a circumferential direction of the bobbin 141 b. The coil winding bodies 141 b, 141 c, and 141 d may further include a terminal portion 141 d to guide a power line connected to the coil 141 c to be drawn or exposed to the outside of the outer stator 141.

The stator core 141 a may include a plurality of core blocks formed, for example, by stacking a plurality of laminations in the circumferential direction. The plurality of core blocks may surround at least a portion of the coil winding bodies 141 b, 141 c, and 141 d.

Stator cover 149 may be provided on one side of the outer stator 141. In other words, one or a first side portion of the outer stator 141 may be supported by the frame 110, and the other or a second side portion thereof may be supported by the stator cover 149.

The stator cover 149 and the frame 110 may be fastened by a cover fastening member or fastener 149 a. The cover fastening member 149 a may extend forward toward the frame 110 through the stator cover 149 and may be coupled to a fastening hole provided in the frame 110.

The inner stator 148 may be fixed to an outer circumference of the frame 110. In addition, the inner stator 148 may be configured by stacking a plurality of laminations in the circumferential direction from the outside of the frame 110.

In summary, as a predetermined current is applied to the coil 141 c, the outer stator 141 and the inner stator 148 may form an electric field. In addition, by such an electric field, the permanent magnet 146 is given an electromagnetic force and can be reciprocated in the axial direction with the piston 130.

A reciprocating speed and distance of the permanent magnet 146 may be changed according to a current value applied to the coil 141 c. In other words, the movement of the piston 130 may be changed according to the current value applied to the motor assembly 140. This will be described hereinafter.

The compressor 10 may further include supporter 137 that supports the piston 130. The supporter 137 may be coupled to the rear side of the piston 130, and the suction muffler 150 may be disposed in the supporter 137 to pass through the supporter 137. The piston flange 132, the magnet frame 138, and the supporter 137 may be fastened by a fastening member or fastener.

Balance weight 179 may be coupled to the supporter 137. A weight of the balance weight 179 may be determined based on an operating frequency range of the compressor main body.

The compressor 10 may further include rear cover 170 coupled to the stator cover 149, extending rearward, and supported by the second support device 185. The rear cover 170 may include three support legs, and the three support legs may be coupled to a rear surface of the stator cover 149. A spacer 181 may be interposed between the three support legs and the rear surface of the stator cover 149. A distance from the stator cover 149 to the rear end portion of the rear cover 170 may be determined by adjusting a thickness of the spacer 181. The rear cover 170 may be spring-supported to the supporter 137.

The compressor 10 may further include an inflow guide portion or guide 156 coupled to the rear cover 170 to guide inflow of the refrigerant into the suction muffler 150. At least a portion of the inflow guide portion 156 may be inserted into the suction muffler 150.

The compressor 10 further includes a plurality of resonant springs 176 a and 176 b whose natural frequencies are adjusted to allow the piston 130 to resonate. The plurality of resonant springs 176 a and 176 b may include first resonant spring 176 a which may be supported between the supporter 137 and the stator cover 149 and second resonant spring 176 b which may be supported between the supporter 137 and the rear cover 170. By the action of the plurality of resonant springs 176 a and 176 b, stable movement of the drive unit reciprocating inside the compressor 10 may be performed and it is possible to reduce vibration or noise generated by movement of the drive unit. The supporter 137 may include a first spring support portion or support 137 a coupled to the first resonant spring 176 a.

The compressor 10 may include a plurality of sealing members or seats 127, 128, 129 a, and 129 b that increases a coupling force between the frame 110 and the components around the frame 110. The plurality of sealing members 127, 128, 129 a, and 129 b may include first sealing member or seal 127 provided at a portion at which the frame 110 and the discharge cover 160 are coupled to each other. The first sealing member 127 may be disposed in a first installation groove of the frame 110.

The plurality of sealing members 127, 128, 129 a, and 129 b may further include second sealing member or seal 128 provided at a portion at which the frame 110 and the cylinder 120 are coupled to each other. The second sealing member 128 may be disposed in a second installation groove of the frame 110.

The plurality of sealing members 127, 128, 129 a, and 129 b may further include third sealing member or seal 129 a provided between the cylinder 120 and the frame 110. The third sealing member 129 a may be disposed in a cylinder groove formed in or at a rear portion of the cylinder 120. The third sealing member 129 a can perform functions of preventing leakage of the refrigerant in a gas pocket formed between the inner circumferential surface of the frame and the outer circumferential surface of the cylinder to the outside and increasing the coupling force between the frame 110 and the cylinder 120.

The plurality of sealing members 127, 128, 129 a, and 129 b may further include fourth sealing member or seal 129 b provided at a portion at which the frame 110 and the inner stator 148 are coupled to each other. The fourth sealing member 129 b may be disposed in a third installation groove of the frame 110. The first to fourth sealing members 127, 128, 129 a, and 129 b may each have a ring shape.

The compressor 10 may further include first support device or support 165 that supports one or a first side of the main body of the compressor 10 and second support device or support 185 that supports the other or a second side of the main body of the compressor 10. The first support device 165 may be disposed adjacent to the second shell cover 103 and coupled to the discharge cover 160 to elastically support the main body of the compressor 10. The second support device 185 may be coupled to the first shell cover 102 and the rear cover 170 to elastically support the main body of the compressor 10.

The first support device 165 may include a first support spring 166 coupled to the spring fastening portion 101 a described with reference to FIG. 3. The second support device 185 may include a second support spring 186 coupled to the cover support portion 102 a described with reference to FIG. 3.

The compressor 10 according to an embodiment may include a bearing flow path formed so that bearing refrigerant is supplied to the piston 130. The bearing refrigerant refers to a refrigerant supplied to the piston 130 to function as a bearing. In other words, the compressor 10 corresponds to an oilless compressor using a refrigerant without adding a lubricant such as oil.

The bearing refrigerant corresponds to some of the refrigerant compressed by the piston 130. The refrigerant compressed by the piston 130 is discharged to the compression space P. Some refrigerant (bearing refrigerant) may be supplied to the piston 130 through the frame 110 and the cylinder 120.

Accordingly, the bearing flow path may include cylinder bearing flow paths 125 and 126 formed in the cylinder 120 and a frame bearing flow path 114 formed in the frame 110. In other words, at least some of the refrigerant compressed by the piston 130 may flow into the cylinder bearing flow paths 125 and 126 and the frame bearing flow path 114 to be supplied to the piston 130.

The frame bearing flow path 114 may be formed through the frame 110. The frame bearing flow path 114 may extend from a front surface of the frame 110 to the outer circumferential surface of the cylinder 120. Referring to FIG. 5, it may be understood that the frame bearing flow path 114 is formed obliquely in the axial direction.

The cylinder bearing flow path may include a gas inlet 126 and a cylinder nozzle 125. The gas inlet 126 may be recessed radially inward from the outer circumferential surface of the cylinder main body 121. In addition, the gas inlet 126 may be configured to have a circular shape along the outer circumferential surface of the cylinder main body 121 based on an axial center axis. A plurality of the gas inlets 126 may be provided. For example, two gas inlets 126 may be provided spaced apart in the axial direction.

The cylinder nozzle 125 may be formed to extend from the gas inlet 126 to an inner peripheral surface of the cylinder main body 121. In particular, the cylinder nozzle 125 may extend radially inward from the gas inlet 126. The cylinder nozzle 125 may be formed very narrow to adjust an amount of the refrigerant flow.

The bearing refrigerant corresponds to some of the refrigerant flowing through the compressor 10. Thus, if the amount of the bearing refrigerant is too large, the amount of refrigerant compressed by the compressor 10 is reduced. Therefore, the amount of the bearing refrigerant may be properly adjusted through the cylinder nozzle 125, for example.

In addition, a gas pocket may be formed between the cylinder 120 and the frame 110. A predetermined bearing refrigerant may flow between the outer circumferential surface of the cylinder main body 121 and the inner circumferential surface of the frame 110. Accordingly, the refrigerant flowing along the frame bearing flow path 114 may flow to the gas inlet 126.

The refrigerant passing through the gas inlet 126 may flow into the space between the inner circumferential surface of the cylinder main body 121 and the outer circumferential surface of the piston main body 131 through the cylinder nozzle 125. The bearing refrigerant may provide a floating force to the piston 130 to perform a function of a gas bearing for the piston 130.

The bearing refrigerant may be supplied to the outer circumferential surface of the piston 130 to space apart the piston 130 from the cylinder 120. Accordingly, friction between the cylinder 120 and the piston 130 may be minimized during movement of the piston 130.

According to an ambient temperature of the compressor 10, the bearing refrigerant may not provide a sufficient floating force to the piston 130. Accordingly, a large problem may occur such that breakage of the piston 130, for example, may occur.

Therefore, the compressor 10 according to embodiments disclosed herein may be controlled to prevent such a problem. This will be described hereinafter.

FIG. 6 is a view illustrating a control configuration of a linear compressor according to an embodiment. As illustrated in FIG. 6, the compressor 10 according to an embodiment may include a controller 200 that controls various components. In addition, the compressor 10 includes a power supply unit or power supply 210 and an input unit or input 220 that transmits a predetermined signal to the controller 200.

The power supply unit 210 may transmit an ON/OFF signal of the compressor 10 to the controller 200. For example, the power supply unit 210 may correspond to a code connected to an external power source or a signal input by a user. According to a signal from the power supply unit 210, the controller 200 may apply and stop applying current to the motor assembly 140.

The input unit 220 may deliver various information necessary for operation to the controller 200. For example, the input unit 220 may include temperature information of a place where the compressor 10 is installed. In addition, the input unit 220 may be understood as a device having a function of transmitting various information such as humidity and load to the controller 200.

In addition, the compressor 10 may include a memory unit or memory 260 that stores predetermined information and a display unit or display 250 that displays predetermined information. The memory unit 260 may be understood as a device in which information necessary for operation of the compressor 10 is stored. For example, the memory unit 260 may store information about a current applied to the motor assembly 140.

The display unit 250 may be understood as a device which provides information related to operation of the compressor 10. In particular, the display unit 250 may a malfunction of the compressor 10, for example, by displaying the operation information of the compressor 10 to a user or an administrator.

The compressor 10 may also include an ambient temperature sensing unit or sensor 230. The ambient temperature sensing unit 230 may be understood as a device that measures ambient temperature. The ambient temperature may correspond to an external temperature of the shell 101. In other words, the ambient temperature may be understood as a temperature of the place where the compressor 10 is installed.

The ambient temperature sensing unit 230 may include a predetermined temperature sensor. The temperature sensor may be attached to the outside of the shell 101 or disposed in a device in which the compressor 10 is installed.

In addition, the compressor 10 may include a current supply unit or supply 240 that supplies a predetermined current to the motor assembly 140. The controller 200 may apply a predetermined current to the motor assembly 140 through the current supply unit 240. The current supply unit 240 may correspond to a device that supplies current to the coil 141 c through the terminal 108 described above.

The controller 200 may determine a current value applied to the motor assembly 140 according to the ambient temperature measured by the ambient temperature sensitive unit 230. This will be described hereinafter.

FIGS. 7 and 8 are views illustrating a control flow of a linear compressor according to an embodiment. FIG. 8 illustrates a state where compressor 10 is turned on and may be understood as an exemplary situation of FIG. 7.

As illustrated in FIG. 7, the ambient temperature is measured (S10). Then, it is determined whether the ambient temperature is equal to or lower than a preset or predetermined safety temperature A (S20). The safety temperature A may be understood as a value stored in the memory unit 260 at a predetermined temperature value. For example, the safety temperature A may be 10 degrees.

When the ambient temperature is equal to or lower than the safety temperature A, the safety current S may be applied to the motor assembly 140 (S30). The safety current S may be understood as a value stored in the memory unit 260 at a predetermined current value. For example, the safety current S may be 1.5 A. The ambient temperature may be measured and it may be determined whether the measured ambient temperature is higher than the safety temperature A (S40). When the ambient temperature is higher than the safety temperature A, application of the safety current S to the motor assembly 140 may be stopped (S50).

In summary, if the ambient temperature is continuously measured, and the measured ambient temperature is equal to or lower than the safety temperature A, the safety current S may be applied. When the measured ambient temperature becomes higher than the safety temperature A, the application of the safety current S may be stopped.

When the compressor 10 is in the OFF state, the safety current S may be applied when the measured ambient temperature is equal to or lower than the safety temperature A. When the measured ambient temperature is higher than the safety temperature A, application of the safety current S may be stopped and the compressor 10 may be turned off.

As illustrated in FIG. 8, when the compressor 10 is in an ON state (S100), a drive current D may be applied to the motor assembly 140 (S110). The drive current D may correspond to a predetermined current value and may correspond to a current value higher than a minimum applied current m and lower than a maximum applied current M (m<M) (m<D<M). In other words, when the drive current D is operated at the minimum applied current m, it can be understood that the compressor 10 is operated at a minimum output. In addition, when the drive current D is operated at the maximum applied current M, it can be understood that the compressor 10 is operated at a maximum output.

The maximum applied current M corresponds to a current value smaller than the safety current S (M<S). For example, if the safety current S is 1.5 A, the maximum applied current M may be 1 A. Accordingly, the drive current D corresponds to a value smaller than 1 A.

The current value applied to the motor assembly 140 may affect a top dead center TDC, a bottom dead center BCD of the piston 130, and a stroke distance corresponding to a distance between the top dead center and the bottom dead center. The greater the current value applied, the longer the stroke distance. Accordingly, when the safety current S is applied rather than when the maximum applied current M is applied to the motor assembly 140, the piston 130 is moved longer in the axial direction.

When the maximum applied current M is applied to the motor assembly 140, the top dead center of the piston 130 is referred to as the maximum top dead center M_TDC, and the bottom dead center is referred to as the maximum bottom dead center M_BDC. In addition, the distance between the maximum top dead center M_TDC and the maximum bottom dead center M_BDC is referred to as a maximum stroke distance.

When the safety current S is applied to the motor assembly, the top dead center of the piston 130 is referred to as a safety top dead center S_TDC, the bottom dead center is referred to as a safety bottom dead center S_BDC. In addition, the distance between the safety top dead center S_TDC and the safety bottom dead center S_BDC is referred to as the safety stroke distance.

As the safety current S corresponds to a current value greater than the maximum applied current M, the stable stroke distance is longer than the maximum stroke distance. In other words, the safety top dead center S_TDC is located axially ahead of the maximum top dead center M_TDC, and the safety bottom dead center S_BDC is located axially rearward of the maximum bottom dead center M_BDC.

The ambient temperature is measured (S120), and it is determined whether the ambient temperature is equal to or lower than the safety temperature A (S130). When the ambient temperature is equal to or lower than the safety temperature A, the safety current S is applied to the motor assembly 140 (S140). As described above, the safety current S corresponds to a current value greater than the drive current D. If the measured ambient temperature is higher than the safety temperature A (S150), the drive current D is applied to the motor assembly 140 (S160).

In summary, regardless of the ON/OFF of the compressor 10, when the ambient temperature is equal to or lower than the safety temperature A, the safety current S is applied to the motor assembly 140. Then, when the ambient temperature is higher than the safety temperature (A), it is driven back to its original state.

When the safety current S is applied, the coil 141 d is heated. That is, the safety current S applies a current value greater than the maximum applied current M designed to produce the maximum output, thereby inducing heat generation of the coil 141 d. In other words, the safety current S is applied not for the purpose of compressing the refrigerant but for the purpose of heating. This is to reduce the amount of refrigerant flowing as the ambient temperature is lowered and to prevent problems caused as the temperature is lowered.

When the ambient temperature is lowered, the compressor 10 is generally turned off or operated at low output. As a result, the amount of refrigerant compressed by the compressor 10 decreases and the amount of the bearing refrigerant decreases. Accordingly, the bearing refrigerant may not be secured in sufficient amount to provide the floating force to the piston 130.

When the ambient temperature is lowered, the temperature of the bearing refrigerant is also lowered. In particular, when the compressor 10 is turned off for a long time, the temperature of the bearing refrigerant may be very low. Accordingly, the bearing refrigerant may be condensed, and the bearing flow path may be blocked by the condensed bearing refrigerant.

In particular, as the cylinder nozzle 125 is formed in a very narrow flow path, the cylinder nozzle 125 may be closed even with a small amount of condensation refrigerant is present. Accordingly, the bearing refrigerant may not flow to the piston 130.

Therefore, when the ambient temperature is very low, the safety current S is applied to heat the coil 141 d. Accordingly, the bearing refrigerant is expanded to provide sufficient floating force to the piston 130 and to prevent condensation thereof.

However, this is merely exemplary and is not limited thereto. For example, a heating unit may be provided at one side of the shell 101 to transfer heat to the bearing refrigerant.

Hereinafter, a case where such a compressor 10 is provided in a refrigerator will be described.

FIG. 9 is a view illustrating a control flow of a refrigerator having a linear compressor according to an embodiment. As illustrated in FIG. 9, an internal temperature and an external temperature of the storage chamber 4 may be measured (S200). The refrigerator 1 may include an internal temperature sensor installed inside of the storage chamber 4 and an external temperature sensor installed outside of the storage chamber 4. For example, the external temperature sensor may be installed in a hinge provided to allow refrigerator door 3 to be rotatably coupled to cabinet 2.

Referring to FIG. 7, the internal temperature sensor may correspond to input unit 220, and the external temperature sensor may correspond to ambient temperature sensing unit 230. In other words, the external temperature of the storage chamber 4 may correspond to the ambient temperature. Hereinafter, for convenience of explanation, the ambient temperature is described as an external temperature.

It is determined whether the internal temperature is equal to or higher than a preset or predetermined temperature B inside of the refrigerator (S210). The temperature B inside of the refrigerator may be understood as a value stored in the memory unit 260 at a predetermined temperature value. In addition, the temperature B may correspond to a value input by a user to the input unit 220. Generally, the temperature B inside the refrigerator may be determined as an initial value by the memory unit 260 and provided to be changeable through the input unit 220.

When the internal temperature is higher than the preset internal temperature B, the drive current D may be applied (S220). As described above, the drive current D corresponds to a current value greater than the minimum applied current m and smaller than the maximum applied current M (m<M) (m<D<M).

It is determined whether the external temperature is lower than a preset or predetermined safety temperature A (S230). When the external temperature is equal to or lower than the preset safety temperature A, the safety current S may be applied (S240). As described above, the safety current S corresponds to a current value greater than the maximum applied current M (M<S). In addition, if the measured external temperature is higher than the safety temperature (A), the application of the safety current S to the motor assembly 140 may be stopped (S260).

In summary, when the measured external temperature is equal to or lower than the safety temperature A, the safety current S is applied regardless of the internal temperature. When the measured outside temperature is higher than the safety temperature A, and when the measured inside temperature is equal to or higher than the temperature B inside the refrigerator, the drive current D is applied. When the measured internal temperature is lower than the temperature B inside of the refrigerator, driving of the compressor 10 is stopped.

In general, as the external temperature of the storage chamber 4 is higher, the output of the compressor 10 is increased. This is because a high external temperature causes a lot of heat loss and the required cold power.

Therefore, the refrigerator 1 according to embodiments also increases the output of the compressor 10 as the external temperature of the storage chamber 4 is higher. In other words, the higher the measured external temperature, the higher the current value applied to the compressor 10, and the lower the measured external temperature, the lower the current value applied to the compressor 10.

However, when the external temperature is very low, the current value applied to the compressor 10 is increased to secure the bearing refrigerant. In other words, the external temperature and the applied current value are proportional to each other, but when the temperature is lower than a specific temperature, the current value is rapidly increased. The relationship between the external temperature and the current value is described on the assumption that there is no change in other conditions.

Through such control, it is possible to ensure sufficient bearing refrigerant even when the external temperature is very low. Accordingly, damage to the piston 130 and its surrounding components may be prevented.

According to embodiments, even when the external temperature is very low, there is an advantage that the linear compressor and the refrigerator may be controlled so that the bearing refrigerant smoothly functions as a bearing. Accordingly, there is an advantage that the bearing refrigerant does not function as a bearing, the bearing flow path is closed or sufficient floating force is not provided to the piston, thereby preventing the piston from being damaged.

In particular, when the external temperature is very low, there is an advantage that the bearing refrigerant can be expanded by heating the coil by applying a safety current higher than the maximum drive current that is generally driven. In addition, by applying the safety current according to the external temperature regardless of the ON/OFF of the linear compressor, there is an advantage that stability may be ensured even when the compressor is off.

Embodiments disclosed herein provide a method for controlling a linear compressor and a refrigerator for ensuring a smooth bearing function of the bearing refrigerant when the ambient temperature is lowered to a predetermined safety temperature or less. In addition, embodiments disclosed herein provide a method for controlling a linear compressor and a refrigerator to heat the coil and transfer heat to the bearing refrigerant, as a safety current higher than the maximum applied current is applied to the motor assembly.

A method for controlling a linear compressor according to embodiments disclosed herein may include measuring an ambient temperature, and when the measured ambient temperature is equal to or lower than a preset or predetermined safety temperature A, applying a safety current S to a motor assembly for driving the piston. If the measured ambient temperature is higher than the safety temperature A, a current lower than the safety current S may be applied to the motor assembly.

The linear compressor may be turned on, and when the measured ambient temperature is higher than the safety temperature A, a drive current D (m<D<M) greater than a minimum applied current m and smaller than a maximum applied current M (m<M) may be applied to the motor assembly. The maximum applied current M may correspond to a current value smaller than the safety current S.

A method for controlling a refrigerator according to embodiments disclosed herein may include measuring an internal temperature and an external temperature of a storage chamber, and when the measured external temperature is lower than a preset or predetermined safety temperature, applying a safety current S to the linear compressor. The method for controlling a refrigerator may include, when the measured internal temperature is equal to or higher than the preset temperature in the refrigerator, applying a drive current D (m<D<M) which is higher than a minimum applied current m and lower than a maximum applied current M (m<M) to the linear compressor. The maximum applied current M may correspond to a current value smaller than the safety current S.

It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

Spatially relative terms, such as “lower”, “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “lower” relative to other elements or features would then be oriented “upper” relative to the other elements or features. Thus, the exemplary term “lower” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It Will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the disclosure. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 

What is claimed is:
 1. A method for controlling a linear compressor including a piston and a bearing flow path configured to supply bearing refrigerant to the piston, the method comprising: measuring an ambient temperature; when the measured ambient temperature is equal to or lower than a predetermined safety temperature, applying a safety current to a motor assembly for driving the piston; and when the measured ambient temperature is higher than the predetermined safety temperature, applying a current lower than the safety current to the motor assembly.
 2. The method of claim 1, further comprising: turning on the linear compressor; and when the measured ambient temperature is higher than the predetermined safety temperature, applying a drive current greater than a minimum applied current and smaller than a maximum applied current to the motor assembly, wherein the maximum applied current is smaller than the safety current.
 3. The method of claim 2, further comprising: after applying the drive current to the motor assembly, again measuring the ambient temperature; when the measured ambient temperature is equal to or lower than the predetermined safety temperature, applying the safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, continuously applying the drive current to the motor assembly.
 4. The method of claim 3, further comprising: after applying the safety current to the motor assembly, again measuring the ambient temperature; when the measured ambient temperature is equal to or lower than the predetermined safety temperature, continuously applying the safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, applying the drive current to the motor assembly.
 5. The method of claim 2, wherein, when the maximum applied current is applied to the motor assembly, the piston is reciprocated between a maximum top dead center and a maximum bottom dead center, wherein, when the safety current is applied to the motor assembly, the piston is reciprocated between a safety top dead center and a safety bottom dead center, and wherein a safety stroke distance which is a distance between the safety top dead center and the safety bottom dead center is longer than a maximum stroke distance which is a distance between the maximum top dead center and the maximum bottom dead center.
 6. The method of claim 5, wherein the piston is reciprocated in an axial direction, wherein the safety top dead center is located in front of the maximum top dead center in the axial direction, and wherein the safety bottom dead center is located at a rear of the maximum bottom dead center in the axial direction.
 7. The method of claim 1, further comprising: turning off the linear compressor; when the measured ambient temperature is equal to or lower than the predetermined the safety temperature, applying a safety current to the motor assembly; after applying the safety current, measuring the ambient temperature; when the measured ambient temperature is equal to or lower than the predetermined safety temperature, continuously applying the safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, stopping applying the safety current to the motor assembly.
 8. The method of claim 1, wherein the bearing flow path includes a cylinder bearing flow path formed in a cylinder in which the piston is received and a frame bearing flow path formed in a frame in which the cylinder is received, wherein the piston is reciprocated by the motor assembly to compress refrigerant, and wherein at least a portion of compressed refrigerant flows into the cylinder bearing flow path and the frame bearing flow path and is supplied to the piston.
 9. The method of claim 8, wherein the cylinder bearing flow path includes: a gas inlet recessed inward from an outer circumferential surface of the cylinder in a radial direction; and a cylinder nozzle extended from the gas inlet to an inner circumferential surface of the cylinder.
 10. The method of claim 1, wherein the motor assembly includes: an outer stator having a coil to which current is applied; an inner stator disposed inside of the outer stator; and a permanent magnet disposed movably inside of the outer stator and the inner stator, the permanent magnet being connected to the piston, wherein, when the safety current is applied to the coil, the bearing refrigerant is expanded by heat generated in the coil.
 11. The method of claim 1, wherein the ambient temperature corresponds to an outer temperature of a shell in which the piston is received and to which a suction pipe and a discharge pipe are coupled through which the refrigerant flows into the shell and is discharged from the shell, respectively.
 12. The method of claim 1, wherein the safety temperature is 10 degrees.
 13. A method for controlling a refrigerator equipped with a linear compressor, the method comprising: measuring an internal temperature and an external temperature of a storage chamber; when the measured internal temperature is equal to or higher than a predetermined temperature in the refrigerator, applying a drive current which is higher than a minimum applied current and lower than a maximum applied current to the linear compressor; and when the measured external temperature is equal to or lower than a predetermined safety temperature, applying a safety current to the linear compressor, wherein the maximum applied current corresponds to a current value smaller than the predetermined safety current.
 14. The method of claim 13, further comprising: when the measured external temperature is equal to or lower than the predetermined safety temperature and the measured internal temperature is equal to or higher than the temperature in the refrigerator, applying the safety current to the linear compressor.
 15. The method of claim 13, further comprising: when the measured external temperature is higher than the predetermined safety temperature and the measured internal temperature is equal to or higher than the predetermined temperature in the refrigerator, applying the drive current to the linear compressor, wherein the higher the external temperature, the greater the current value of the drive current.
 16. A method for controlling a linear compressor, the linear compressor including a shell having suction and discharge pipes through which a fluid flows into and out of the shell, a frame received by the shell, a cylinder received by the frame, a piston received by the cylinder, a motor assembly that drives the piston to reciprocate axially within the cylinder to compress the fluid, and a bearing flow path that extends through the frame and the cylinder and configured to supply bearing fluid to the piston, the method comprising: measuring an ambient temperature corresponding to an outer temperature of the shell; when the measured ambient temperature is equal to or lower than a predetermined safety temperature, applying a safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, applying a current lower than the safety current to the motor assembly.
 17. The method of claim 16, further comprising: turning on the linear compressor; and when the measured ambient temperature is higher than the predetermined safety temperature, applying a drive current greater than a minimum applied current and smaller than a maximum applied current to the motor assembly, wherein the maximum applied current is smaller than the safety current.
 18. The method of claim 17 further comprising: after applying the drive current to the motor assembly, again measuring the ambient temperature; when the measured ambient temperature is equal to or lower than the predetermined safety temperature, applying the safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, continuously applying the drive current to the motor assembly.
 19. The method of claim 18, further comprising: after applying the safety current to the motor assembly, again measuring the ambient temperature; when the measured ambient temperature is equal to or lower than the predetermined safety temperature, continuously applying the safety current to the motor assembly; and when the measured ambient temperature is higher than the predetermined safety temperature, applying the drive current to the motor assembly.
 20. The method of claim 16, wherein the safety temperature is 10 degrees. 